1. Field of the Invention
The invention relates to a feed pump with at least one driven impeller rotating in a pump casing, wherein a plurality of rings of blade chambers are arranged on at least one end face of the impeller, feed channels are arranged opposite the rings of blade chambers in the wall of the pump casing, and guide blades delimit the blade chambers of the impeller.
2. Description of the Related Art
Feed pumps with impellers having plural ring blade chambers are often used for feeding fuel out of a fuel tank in present-day motor vehicles and are known from practice. The known feed pump includes two rings of blade chambers, one concentrically surrounding the other, on a common impeller. When the impeller rotates, the fuel passes via an inlet channel first into a radially inner one of the feed channels and subsequently into a radially outer one of the feed channels. The pump consequently has two pumping stages.
Furthermore, another known feed pump is made with two impellers, each having a ring of blade chambers. In this known device, each impeller forms a pumping stage of the feed pump.
A problem associated with the known feed pumps is that they generate very high noise emissions. The noise emissions create a disturbing whistling sound.
It is an object of the present invention to provide a feed pump having an impeller with plural rings of blade chambers so that the feed pump generates noise emission causing particularly little disturbance.
The object is met according to the present invention by arranging angular intervals between adjacent guide blades relative to one another and on different rings to vary slightly in each case according to the rules of stochastic distribution, i.e., the angular intervals between successive adjacent guide blades vary by a random amount.
The slight variation in angular intervals between guide blades keeps the noise emissions in each of the rings of guide blades particularly low. Accordingly, none of the rings of guide blades generates a whistling sound. The variation in the angular intervals of the guide blades of the various rings prevents the noise emissions of each guide blade from adding up. The rings of guide blades therefore in each case generate noise emissions at different frequencies. Therefore, the noise emissions of the feed pump according to the present invention are distributed over a wide range of the audible frequency spectrum and are detected by the human ear as a uniform murmur. The feed pump according to the present invention consequently generates noise emissions which cause particularly little disturbance.
According to an embodiment of the present invention, a contribution to the particularly wide distribution of the noise emissions over the audible frequency spectrum is made if the angular intervals of the guide blades of different rings vary in different ranges.
According to another embodiment of the present invention, overlaps of noise emissions of two rings of guide blades which may be generated accidentally due to the variation in the angular intervals, may be avoided in a simple way if the number of guide blades of the different rings varies.
The feed pump according to the present invention has, along with low disturbing noise emissions, particularly high efficiency if the number of guide blades of a radially inner one of two rings is smaller than the number of guide blades in the radially outer one of the two rings.
According to further embodiment of the present invention, noise emissions generated due to the rings of guide blades influencing one another via the fuel to be fed is avoided in a simple way if each feed channel is provided for connection to a specific consumer. For example, one feed channel may lead to a suction jet pump arranged within the fuel tank while the other feed channel is connected to a forward-flowline leading to an internal combustion engine of the motor vehicle. Moreover, one feed channel may be provided for suction intake directly from the fuel tank and the other feed channel for suction intake from a baffle. As a result, the flow of fuel from one ring of guide blades to a further ring is prevented, thereby avoiding the transmission and intensification of the noises within the feed pump.
The feed pump according to the present invention has particularly low noise emissions, along with high efficiency, if the angular intervals of the radially outer ring of guide blades of two rings vary relative to one another in the range of 8xc2x0 to 12xc2x0.
A contribution to a further reduction in the noise emissions of the feed pump according to the invention is made if the angular intervals of the radially inner ring of guide blades of two rings vary relative to one another in the range of 16xc2x0 to 20xc2x0.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.